Dissertations / Theses on the topic 'Local buckling'
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1
Hakmi, M. R. "Local buckling of sandwich panels." Thesis, University of Salford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234622.
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Clarin, Mattias. "Plate buckling resistance : patch loading of longitudinally stiffened webs and local buckling /." Luleå : Division of Structural Engineering - Steel Structures, Department of Civil, Mining and Environmental Engineering, Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1544/2007/31/LTU-DT-0731-SE.pdf.
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Yoon, Soon Jong. "Local buckling of pultruded I-shape columns." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20118.
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Da, Silva Vellasco Pedro Colmar Goncalves. "Local web buckling in tapered composite beams." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/29499.
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Recent demand for very heavily serviced widespan office floors has led, as a natural development of the concept of haunched and tapered frames, to the use of composite flooring systems supported by tapered (varying web depth) beams. These systems are very attractive from an economic point of view, combining wide spans, rapid erection and easy access to services between the shallow parts of the beam and the ceiling below. One of the most pressing needs is for a better understanding of the local buckling behaviour of the relatively deep slender web at changes of slope in the lower flange, in particular at the slope change which occurs at the centre of a beam whose depth increases linearly from each support. In the past, with plate girders, this failure mechanism was less relevant than lateral torsional buckling. With the substantial top flange of a composite section, lateral buckling is less likely, and local buckling more likely to govern the design. The tapered beam sections are fabricated from plates by welding and are susceptible to imperfection effects and residual stresses. These phenomena may interact with the localized compressive stress field which is generated in the web at any slope change in the flange to cause local web buckling. The provision of local stiffening is technically feasible, but very expensive. The beam itself is produced fully automatically and the subsequent hand installation of stiffeners consumes man-hours out of all proportion to the weight of steel involved. The prime objective of the present study was to iucntify the relative importance of several parameters that influence the phenomenon, such as angle of taper, web thickness, flange area and others. For practical reasons, the experiments were executed at half-scale and the models simulated the concrete slab of the composite beam by a heavy steel top flange. Three tapered models have been tested with different web thicknesses i.e, 3, 5, and 7 millimetres. Three more specimens with different plastic neutral axis positions were also tested. An extensive parametric study has been made using a non-linear elastoplastic finite element program. This study covered practical ranges of the important parameters including the area of the tension flange and the position of the plastic neutral axis. Moment-rotation relations, peak moments and failure mechanisms have been predicted. Very good correlation was obtained between the results of the parametric study and the experiments. It has become apparent that in the great majority of practical cases it is possible to avoid the use of the expensive hand welded stiffeners. A design formulation has been developed to produce a very simple test of the need for stiffeners.
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Ghosh, Biswarup. "Consequences of Simultaneous Local and Overall Buckling in Stiffened Panels." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/31803.
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In this thesis improved expressions for elastic local plate buckling and overall panel buckling of uniaxially compressed T-stiffened panels are developed and validated with 55 ABAQUS eigenvalue buckling analyses of a wide range of typical panel geometries. These two expressions are equated to derive a new expression for the rigidity ratio (EIx/Db)CO that uniquely identifies ¡°crossover¡± panels ¨C those for which local and overall buckling stresses are the same. The new expression for (EIx/Db)CO is also validated using the 55 FE models. Earlier work by (Chen, 2003) had produced a new step-by-step beam-column method for predicting stiffener-induced compressive collapse of stiffened panels. An alternative approach is to use orthotropic plate theory. As part of the validation of the new beam-column method, ABAQUS elasto-plastic Riks ultimate strength analyses were made for 107 stiffened panels ¨C the 55 crossover panels and 52 others. The beam-column and orthotropic approaches were also used. A surprising result was that the orthotropic approach has a large error for crossover panels whereas the beam-column method does not. Some possible reasons for this are suggested. Collapse patterns for the crossover panels are studied and classified from von Mises stress distribution at collapse. The collapse mechanism and load-deflection diagrams suggest stable inelastic post collapse behavior for most panels and an abrupt drop in load carrying capacity in only nine of the 55.Master of Science
6
Clarin, Mattias. "High strength steel : local buckling and residual stresses." Licentiate thesis, Luleå, 2004. http://epubl.luth.se/1402-1757/2004/054.
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Bonanni, David L. "Local buckling and crippling of composite stiffener sections." Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/80050.
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The local buckling, postbuckling, and crippling (failure) of channel, zee, and I- and J-section stiffeners made of AS4/3502 graphite-epoxy unidirectional tape are studied by experiment and analysis. Thirty-six specimens were loaded in axial compression as intermediate length columns. Examination of the experimental results indicates the existence of a number of damage initiation modes, all of which involve either delamination in some part of the specimen or local material strength failure in a comer of the specimen. The ratio of the flange width to thickness has a strong influence on the buckling stress and damage initiation mode. The inner corner radius strongly affects the buckling and crippling stresses for the I- and J-section specimens.
Comparison of the numerical results from a computer code for shell analysis (STAGS) with experimental data shows good correlation prior to buckling and at the buckling load, but diminished agreement in the postbuckling region. This lack of postbuckling correlation is attributed to the neglecting of transverse shearing deformations in the structural theory, inaccuracies in the modeling of in-plane boundary conditions, and damage initiation in the experimental specimens. A plane stress failure analysis for five of the specimens shows the compressive fiber mode criterion of Hashin correlates reasonably well with the first detectable damage event. Equilibrium is used to develop interlaminar stress equations for classical laminated plate theory that require high order derivatives of the displacements. Derivatives computed from discrete displacement data using the Discrete Fourier Transform are inaccurate due to the Gibbs phenomenon.Master of Science
8
Dardano, Nicola. "Delamination of thin layers promoted by local buckling." Thesis, IMT Alti Studi Lucca, 2022. http://e-theses.imtlucca.it/363/1/Dardano_phdthesis.pdf.
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This dissertation investigates the combined phenomena of
buckling and fracture, which occur in thin superficial layers subjected to compressive forces. As a representative case, the four-point bending test on laminated specimens with midspan, through-the-width delaminations, is taken into consideration: a mechanical model of the test was developed and experimental tests on carbon fiber laminates were conducted. The thesis is subdivided into six Chapters. Chapter 1 presents a general introduction to the investigated problem. Chapter 2 illustrates the state of the art on delamination in composite materials with focus on buckling-driven delamination and four-point bending tests. Chapter 3 illustrates the experimental Mode II fracture toughness characterization of the carbon fiber laminates investigated in the thesis. In Chapter 4, the experimental campaign with four-point bending tests is illustrated. Chapter 5 presents the analytical model to simulate and interpret the four-point bending tests. Chapter 6 shows a comparison between the analytical prediction and the experimental evidence. In Chapter 7, results are summarized and future developments are outlined.
9
Becque, Jurgen. "The interaction of local and overall buckling of cold-formed stainless steel columns." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/3772.
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Abstract: The objective of this research is to investigate the interaction of local and overall flexural buckling in cold-formed stainless steel columns. Literature study exposes a lack of understanding of this subject and a need for experimental data, particularly on the local-overall interaction buckling of stainless steel open sections. Two separate experimental programs were therefore carried out. The first program included 36 tests on pin-ended lipped channel columns. Three alloys were considered: AISI 304, AISI 430 and 3Cr12. The specimens were designed to fail by local-overall interaction buckling in the inelastic stress range, thus highlighting the non-linear behaviour of stainless steel. Half of the specimens were tested under a concentric load. The other half had the load applied with a nominal eccentricity of Le/1500. The test results demonstrate the imperfection sensitivity of local-overall interaction buckling and illustrate the shift in effective centroid in pin-ended columns with singly symmetric cross-section. The second experimental program studied local-overall interaction buckling in 24 pin-ended stainless steel I-section columns. The specimens consisted of plain channels connected back-to-back using sheet metal screws. Two alloys were considered: AISI 304 and AISI 404. Local and overall imperfections were carefully measured in both experimental programs. Extensive material testing was carried out on the alloys employed in the experimental program, in order to determine tensile and compressive material properties, anisotropic parameters and enhanced corner properties. A detailed finite element model is presented, which includes non-linear material behaviour, anisotropy, increased material properties of the corner areas and local and overall imperfections. The model was verified against the two aforementioned experimental programs and against additional data available in literature on stainless steel SHS columns. The model yielded excellent predictions of the specimen failure mode, ultimate strength and load-deformation behaviour. The finite element model was used to generate additional data for stainless steel columns with lipped channel, plain channel, SHS and I-shaped cross-section, failing by local-overall interaction buckling. The parametric studies covered the practical ranges of overall and cross-sectional slenderness values. The Australian/New Zealand, European and North American standards for stainless steel were evaluated using the available data. The comparison reveals an inability of the design codes to properly account for the interaction effect as the cross-sectional slenderness increases. Predictions are unsafe for I-section columns with intermediate or high cross-sectional slenderness. A direct strength method is proposed for stainless steel columns, accounting for the local-overall interaction effect. The method offers a simple design solution which fits within the framework of the current Australian and North-American standards.
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Becque, Jurgen. "The interaction of local and overall buckling of cold-formed stainless steel columns." University of Sydney, 2008. http://hdl.handle.net/2123/3772.
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PhDAbstract: The objective of this research is to investigate the interaction of local and overall flexural buckling in cold-formed stainless steel columns. Literature study exposes a lack of understanding of this subject and a need for experimental data, particularly on the local-overall interaction buckling of stainless steel open sections. Two separate experimental programs were therefore carried out. The first program included 36 tests on pin-ended lipped channel columns. Three alloys were considered: AISI 304, AISI 430 and 3Cr12. The specimens were designed to fail by local-overall interaction buckling in the inelastic stress range, thus highlighting the non-linear behaviour of stainless steel. Half of the specimens were tested under a concentric load. The other half had the load applied with a nominal eccentricity of Le/1500. The test results demonstrate the imperfection sensitivity of local-overall interaction buckling and illustrate the shift in effective centroid in pin-ended columns with singly symmetric cross-section. The second experimental program studied local-overall interaction buckling in 24 pin-ended stainless steel I-section columns. The specimens consisted of plain channels connected back-to-back using sheet metal screws. Two alloys were considered: AISI 304 and AISI 404. Local and overall imperfections were carefully measured in both experimental programs. Extensive material testing was carried out on the alloys employed in the experimental program, in order to determine tensile and compressive material properties, anisotropic parameters and enhanced corner properties. A detailed finite element model is presented, which includes non-linear material behaviour, anisotropy, increased material properties of the corner areas and local and overall imperfections. The model was verified against the two aforementioned experimental programs and against additional data available in literature on stainless steel SHS columns. The model yielded excellent predictions of the specimen failure mode, ultimate strength and load-deformation behaviour. The finite element model was used to generate additional data for stainless steel columns with lipped channel, plain channel, SHS and I-shaped cross-section, failing by local-overall interaction buckling. The parametric studies covered the practical ranges of overall and cross-sectional slenderness values. The Australian/New Zealand, European and North American standards for stainless steel were evaluated using the available data. The comparison reveals an inability of the design codes to properly account for the interaction effect as the cross-sectional slenderness increases. Predictions are unsafe for I-section columns with intermediate or high cross-sectional slenderness. A direct strength method is proposed for stainless steel columns, accounting for the local-overall interaction effect. The method offers a simple design solution which fits within the framework of the current Australian and North-American standards.
11
Bock, Montero Marina. "Web crippling and local buckling response of stainless steel sections." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/285582.
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This thesis examines the response of stainless steel members when subjected to transverse and normal forces triggering the instability phenomena called web crippling and local buckling, respectively. Currently, the part of Eurocode dealing with stainless steel, EN 1993-1-4 (2006) misses design provisions for web crippling and the applicability of some of its aspects is yet to be fully verified especially for application to ferritic stainless steel.
The first part of the thesis laid in the development of design equations for the treatment of web crippling in stainless steel sections which are currently designed following specifications given in EN 1993-1-3 (2006) for cold-formed carbon steel. Two design approaches were derived covering austenitic and ferritic stainless steels: an empiric equation, in line with the current provisions for web crippling design given in EN 1993-1-3 (2006); and an alternative semi-empiric design method based on strength curves which enables a better understanding of the phenomenon and showed to significantly improve web crippling predictions.
For the second part of the thesis, the applicability of the local buckling design provisions given in EN 1993-1-4 (2006) to ferritic stainless steel was examined giving focus to the slenderness limits and the effective width equations. The results showed that EN 1993-1-4 (2006) can safely be applied to ferritic stainless steel, though the code is rather conservative in comparison with other methods. Finally, a modification of the effective width equation incorporating element interaction effects was proposed which allows an improvement of cross-section capacity predictions and enables to amend the effective width method to the same level of alternative design approaches but promoting the use of the concepts currently considered in Eurocode.Esta tesis estudia la respuesta estructural de elementos de acero inoxidable sometidos a fuerzas transversales i normales que desencadenan los fenómenos de inestabilidad llamados web crippling y local buckling, respectivamente. Actualmente, la parte de Eurocódigo que contempla los aceros inoxidables, el EN 1993-1-4 (2006) carece de ecuaciones de diseño para web crippling y la aplicabilidad de algunas de sus especificaciones necesita ser validada especialmente para los aceros inoxidables ferríticos. La primera parte de esta tesis se focaliza en el desarrollo de ecuaciones de diseño para el tratamiento del web crippling en secciones de acero inoxidable que actualmente se diseñan siguiendo las especificaciones dadas en EN 1993-1-3 (2006) para acero al carbono conformado en frío. Dos métodos de diseño para los aceros inoxidables austeníticos y ferríticos: una ecuación empírica en línea con la actual dada en EN 1993-1-3 (2006); y un método de diseño semi-empírico basado en curvas de resistencia que permite entender mejor el fenómeno y muestra una mejora importante de las predicciones a web crippling. Para la segunda parte de la tesis, se ha estudiado la aplicabilidad de las actuales especificaciones para el diseño a local buckling dadas en EN 1993-1-4 (2006) a los aceros inoxidables ferríticos focalizándose en los límites de esbeltez y las ecuaciones de ancho eficaz. Los resultados mostraron que EN 1993-1-4 (2006) puede ser aplicado a los aceros inoxidables ferríticos, aunque el código es bastante conservador en comparación con otros métodos de diseño. Finalmente, se propuso una modificación de la ecuación del ancho eficaz que incorpora la interacción entre los elementos de la misma sección y que permite, además de mejorar las predicciones de la resistencia seccional, llevar el método del ancho eficaz hasta el mismo nivel que otros métodos de diseño pero ensalzando el uso de los conceptos actualmente considerados en Eurocódigo
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Jeevaharan, Manohara. "Local buckling behaviour and design of sandwich panels in buildings." Thesis, Queensland University of Technology, 1997. https://eprints.qut.edu.au/35998/1/35998_Jeevaharan_1997.pdf.
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Sandwich construction is increasingly used as wall and roof claddings for building
structures. Typically, a cladding panel may consist of two plane or profiled metal
faces with a plastic foam core. The core may be polystyrene or polyurethane.
When such a panel subject to static loading due, for instance, to wind uplift or
temperature gradient, one face is compressed and becomes liable to local
buckling. If this face has a trapezoidal or similar profile the failure mode is
similar to that for profiled steel sheeting, but the failure stress is enhanced by the
presence of the core. The compressed face element first forms a series of buckling
waves which increase in amplitude in the postbuckling phase. Failure take place
when one buckle in the region of maximum bending moment cripples.
This thesis extends the European design recommendations to validate their
research for Australian sandwich panels made of high strength steel and
polystyrene foam core. European design recommendations for foam filled steel
members are based on polyurethane foam core and low tensile steel. In order to
verify the European design recommendations for high tensile steel and
polystyrene foam core, experimental tests and finite element analysis were
conducted. Steel plate elements with and without foam core were used in the
investigation, with varying width to thickness (b/t) ratio (105 to 513) and grade
(G250 and G550) of steel. Buckling stress and buckling shape as well as ultimate
stress and the associated stress versus out-of-plane deflection curves were
produced.
Finite element analyses and experiments illustrated the inherent benefits of
composite foam filled steel members. The improvement of the buckling
coefficient, K, for thin-walled steel plate elements was demonstrated. Each width to thickness (bit) ratio had a specific K value that increased with increasing width
to thickness (b/t) ratio. Results obtained from this investigation showed that the
European buckling and ultimate strength design equations can be satisfactorily
used for the Australian sandwich panels.
13
Chung, Kwok Fai. "The elastic distortional and local plate buckling of slender web beam." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/7860.
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Myrholm, Brian W. "Local buckling and fracture behaviour of line pipe under cyclic loading." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ60477.pdf.
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Kandil, Kamel Sayed Ahmed. "Interaction between local and Euler buckling modes in thin-walled columns." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254398.
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Zainal, Abidin Ahmad Razin. "Modelling of local elastic buckling for steel beams with web openings." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/12789.
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This work is mainly concerned with the development of sophisticated yet efficient methods for assessing the elastic buckling of steel beams with web openings, focussing on local buckling effects in the web region. A new computational method is proposed which extends the use of the Element Free Galerkin (EFG) method for the numerical discretisation combined with a simplified buckling assessment approach based on the Rotational Spring Analogy (RSA). The new approach considers several potential simplifications offering a balance between computational efficiency and accuracy in local buckling analysis. In the present EFG/RSA method, considerable advantage is established by separating the planar and out-of-plane responses. Planar analysis is further enhanced using modular concepts, where the beam is divided into unit cells, each of which resembles a super-element with a reduced number of freedoms, and solved using a standard discrete procedure. As for the out-of-plane analysis, the application of a ‘local region’ is adopted to significantly reduce the size of the original buckling problem. Finally, local buckling assessment is conducted using an effective approach that utilises an iterative procedure based on a rank 2 reduced eigenvalue problem along with a shifting local region. Several illustrative examples are provided which highlight the efficiency and accuracy of the developed approach in comparison with detailed nonlinear finite element analysis performed using ADAPTIC, and which demonstrate general applicability to local buckling analysis of steel beams with web openings of various shapes and sizes. This work also considers the development of a simplified design-oriented method which is presented particularly for web-post buckling. Towards this end, a simplified analytical model is proposed based on an analogy with equivalent rectangular thin beams (RTB), where a semi-empirical approach is used to calibrate the suggested formulation against the results obtained from the numerical work performed earlier.
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Masri, Haji Mohammad Khairul Ja'afar Awang Haji. "Elastic properties and local buckling of pultruded fibre reinforced plastic profiles." Thesis, Cardiff University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548179.
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Slyh, Caleb E. "Investigation into POR-14-0630 Bridge Pile Failures." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1553874013897449.
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Smith, Frank Harrison. "Elastic buckling solutions for thin-walled metal columns with perforation patterns." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23680.
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Presented are approximate finite strip methods for use in predicting elastic buckling strength of cold-formed steel columns. These methods were developed by examining elemental behavior of cross-sections in eigen-buckling analyses and validated using a large database of finite element rack-type columns with perforation patterns. The influence of perforations is accounted by reduced thicknesses related to the plate buckling coefficient and transverse web rotational stiffness in the prediction of local and distortional buckling respectively. Global buckling prediction including the influence of perforations uses critical elastic loads of an unperforated section multiplied by the ratio of weighted to gross cross-sectional moment of inertia for flexural buckling and the ratios of weighted to gross cross-sectional warping torsion constant and weighted to gross St. Venant torsional constant for flexural-torsional buckling. Concern for end-user was given and methods are presented in a way for incorporation into governing design standards. Data to support these findings are available at http://hdl.handle.net/10919/23797Master of Science
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Seresta, Omprakash. "Buckling, Flutter, and Postbuckling Optimization of Composite Structures." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/26401.
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This research work deals with the design and optimization of a large composite structure. In
design of large structural systems, it is customary to divide the problem into many smaller
independent/semi-independent local design problems. For example, the wing structure design
problem is decomposed into several local panel design problem. The use of composite
necessitates the inclusion of ply angles as design variables. These design variables are discrete
in nature because of manufacturing constraint. The multilevel approach results into
a nonblended solution with no continuity of laminate layups across the panels. The nonblended
solution is not desirable because of two reasons. First, the structural integrity of
the whole system is questionable. Second, even if there is continuity to some extent, the
manufacturing process ends up being costlier.
In this work, we develop a global local design methodology to design blended composite
laminates across the whole structural system. The blending constraint is imposed via a guide
based approach within the genetic algorithm optimization scheme. Two different blending
schemes are investigated, outer and inner blending. The global local approach is implemented
for a complex composite wing structure design problem, which is known to have a strong
global local coupling. To reduce the computational cost, the originally proposed local one
dimensional search is replaced by an intuitive local improvement operator. The local panels
design problem arises in global/local wing structure design has a straight edge boundary
condition. A postbuckling analysis module is developed for such panels with applied edge
displacements. A parametric study of the effects of flexural and inplane stiffnesses on the
design of composite laminates for optimal postbuckling performance is done. The design
optimization of composite laminates for postbuckling strength is properly formulated with
stacking sequence as design variables.
Next, we formulate the stacking sequence design (fiber orientation angle of the layers) of
laminated composite flat panels for maximum supersonic flutter speed and maximum thermal
buckling capacity. The design is constrained so that the behavior of the panel in the vicinity
of the flutter boundary should be limited to stable limit cycle oscillation. A parametric study
is carried out to investigate the tradeoff between designs for thermal buckling and flutter.
In an effort to include the postbuckling constraint into the multilevel design optimization
of large composite structure, an alternative cheap methodology for predicting load paths
in postbuckled structure is presented. This approach being computationally less expensive
compared to full scale nonlinear analysis can be used in conjunction with an optimizer for
preliminary design of large composite structure with postbuckling constraint. This approach
assumes that the postbuckled stiffness of the structure, though reduced considerably, remains
linear. The analytical expressions for postbuckled stiffness are given in a form that can
be used with any commercially available linear finite element solver. Using the developed
approximate load path prediction scheme, a global local design approach is developed to
design large composite structure with blending and local postbuckling constraints. The
methodology is demonstrated via a composite wing box design with blended laminates.Ph. D.
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Kusyilmaz, Ahmet. "Finite Element Study On Local Buckling And Energy Dissipation Of Seismic Bracing." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609662/index.pdf.
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Seismic provisions for steel buildings present limiting width-thickness and slenderness ratios for bracing members. Most of these limits were established based on experimental observations. The number of experimental studies is limited due to the costs associated with them. With the rapid increase in computing powerhowever, it is now possible to conduct finite element simulation of brace components using personal computers. A finite element study has been undertaken to evaluate the aforementioned limits for pin-ended pipe section steel braces. Fifty four tubular pipe brace models possessing different diameter-to-thickness ratios varying from 5 to 30 and slenderness ratios varying from 40 to 200 were analyzed. The effect of cyclic hardening modulus on the response of braces was explored. In all analysis, the models were subjected to reversed cyclic displacements up to ten times the yield displacement. Local buckling was traced during the loading history using a criterion based on local strains. Results are presented in terms of the ductility level attained by the member at the onset of local buckling. It is shown that local buckling of the section is influenced by the diameter-to-thickness and the slenderness ratios of the member. Moreover, the amount of hardening modulus was found to affect the local buckling response significantly. The need to include this material property into seismic provisions is demonstrated. Finally, the hysteretic energy dissipated by the member was quantified for each displacement excursion.
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Vakiener, Adam R. "Preliminary investigation of flange local buckling in pultruded wide flange structural shapes." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/19562.
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OLIVEIRA, JULIA PITHAN DE. "DESIGN EQUATIONS FOR LOCAL BUCKLING OF CASTELLATED BEAMS SUBJECTED TO PURE BENDING." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36634@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
PROGRAMA DE EXCELENCIA ACADEMICA
A motivação para este trabalho é desenvolver equações simples, porém suficientemente precisas, que possam ser usadas para projetos de vigas casteladas submetidas à flexão pura, considerando a contribuição do conjunto mesa-alma na flambagem local do elemento. Métodos energéticos - Quociente Rayleigh - são adotados para determinar a equação da tensão crítica aproximada. Neste método, a energia de deformação e o trabalho externo são calculados assumindo uma forma de deflexão aproximada, cinemática admissível e contínua. Assim, a precisão do resultado depende da qualidade da forma de deflexão adotada. Estas funções de forma foram escolhidas com base nos resultados obtidos a partir de modelos numéricos criados usando o software ABAQUS e verificados com o software GBTUL, considerando para analise a interação completa entre a alma e a mesa. As expressões desenvolvidas foram baseadas em aproximações clássicas de estabilidade de placas, validadas com estudos paramétricos realizados com os softwares ABAQUS e GBTUL. Os resultados indicaram que a equação proposta pode efetivamente calcular a tensão crítica relativa a instabilidade local de vigas casteladas. A expressão validada e os limites associados são destinados a ser gerais dentro dos limites típicos das aplicações práticas.
The motivation for this work is to develop a simple yet sufficiently accurate equation that can be used in the design of castellated beams subjected to pure bending, considering the contribution of the web-flange coupling effect in the local buckling. To accomplish this, an energy method - Rayleigh quotient - is adopted to determine the approximate critical stress equation. In this method, the strain energy and the potential work are calculated for an assumed approximate and kinematically admissible continuous deflected shape. Thus, the accuracy of the result is dependent on the quality of the assumed buckled shape. These shape functions were chosen based on the results obtained from numerical models created using ABAQUS software and verified with GBTUL, considering full interaction between web and flange. The developed closed-form expressions were based on classical plate stability approximations, validated with parametric studies performed using ABAQUS and GBTUL. The results indicate that the proposed equation can effectively calculate the critical stress of castellated beams due to local instability. The validated expression and its associated limits are intended to be general within the typical limits of practical applications.
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Cai, Minjie. "Buckling strength of steel thin cylindrical shells under elevated local axial compression." Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/10848.
Full textAbstract:
First, the buckling analyses of perfect cylinder under various uniform/non-uniform axial compression were performed using the finite element method in order to obtain convergence mesh for further study, to find the reference elastic critical load, and to explore the accuracy of the loading and boundary conditions applied. Linear elastic analysis of perfect cylinder under local elevated axial compression was presented second. The meridional membrane stress distribution in the midplane, which subjected to highly elevated stresses of the whole cylinder, was examined in detail and a linear buckling analysis was performed for the buckling strength of the cylinder limited in the small deflections, geometrically and materially linear range. Two different buckling phenomena were identified, with corresponding and distinct buckling mode forms, by using the deflected shapes and axial membrane stress distribution of various geometry and loading configurations. The introduction of this notion is a key feature of the whole study. Third, a modified RIKS analysis was performed to get the load-displacement curve for some representative cases in order to deal with possible instabilities in the extent of geometric non-linearity as well as material non-linearity with and without imperfections. A new self-design approach was set up to obtain the critical buckling strength in the geometrically non-linear domain more efficiently. Geometrically nonlinear elastic analyses were performed afterwards, using large deflection theory. Both perfect and imperfect cylinders were studied under various geometric and loading configurations. This provided the database for the following sets of simply formulae aiming for design purpose. The influence of material non-linearity was studied via some representative cases. Fourth, the stress pattern in the pre-buckling state before buckling under local elevated axial compression was studied to get the relationship between the high local axial stresses and the buckling strength.
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Haidarali, Mohammad Reza. "Local and distortional buckling behaviour of cold-formed steel Z section beams." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6992.
Full textAbstract:
The economic use of cold-formed steel members means that buckling and the possible loss of effectiveness it produces are important features of design. Cross-sectional instabilities in laterally-restrained cold-formed steel beams include local and distortional buckling. The prediction of the true buckling behaviour of cold-formed steel beams accounting for all governing features such as geometrical imperfections, spread of yielding, postbuckling etc. has been possible with the development of advanced numerical modelling. In this thesis, the finite element (FE) method (ABAQUS) has been used to develop numerical analyses to study the buckling behaviour of laterally-restrained cold-formed steel lipped Z-section beams. The FE models were verified against a series of four-point bending tests available from previous research, with special references to material and geometrical nonlinearities. Two sets of analyses have been conducted: FE analyses allowing for both local and distortional buckling and ones allowing for local buckling while distortional buckling is restrained using appropriate boundary conditions. For the former, the controlling buckling mode (local, distortional or combined) at different stages of loading (up to, at and beyond maximum load) has been realized. Comparing the results of two sets of analyses, the effect of distortional buckling on performance for different geometric proportions has been studied. The effect of the lip size, flange width, angle of inclination of the edge stiffener (lip), size and position of the intermediate stiffener and material strength as well as the interaction between them on both the ultimate strength and the buckling of cold-formed Z-section beams has been investigated. Limits for optimum design of the section were proposed. Depending on the geometric properties and material strength of the section, transitions between local, distortional and combined local/distortional buckling were observed. The lip/flange interaction including the interaction between the edge stiffener (lip) and the intermediate stiffener was the key governing feature of behaviour. The effect of the linear moment gradient and sharply varying bending moment on both the ultimate strength and the buckling of cold-formed Z sections was investigated. The latter occurred in two-span continuous beams subject to uniformly distributed loading. The results of moment gradient cases were compared with those of pure bending cases. The suitability of the design treatments available in Eurocode 3 (EC3) for local, combined local/distortional and distortional buckling of cold-formed Z-section beams was assessed. Overall, the EC3 predictions for cross-sectional bending resistances were unconservative. Shortcomings were identified and some suggestions for improvements were made. This included improvements in plate buckling factors for edge-stiffened compression flanges.
26
Shin, Youngwon. "Analytic shape sensitivities and approximations of local and global airframe buckling constraints /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9984.
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Qin, Yi. "Numerical analysis of inelastic local web buckling capacity of coped steel I-beam." Thesis, University of Macau, 2012. http://umaclib3.umac.mo/record=b2586272.
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Toneff, Janine Diana. "Local and overall buckling of thin-walled beams and columns using finite elements." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26334.
Full textAbstract:
Steel members with open thin-walled cross sections are used extensively in civil engineering structures. In addition to overall instability, (Euler buckling, torsional buckling, lateral-torsional buckling, etc.), the thin plates making up the cross section may themselves be susceptible to local plate buckling. The possible interaction of these two modes of buckling and its effect on member stability and strength is therefore of interest in the analysis of such members. The purpose of this thesis is to develop a tool for this type of analysis by adapting a finite element for a thin-walled beam-column of arbitrary cross section to include 'local' degrees of freedom to allow for cross section distortion. The formulation will involve geometric nonlinearities due to large displacements and rotations, but material behaviour will be limited to the linear elastic case.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
29
Nassirirad, Arash. "The effects of corner radii on the local buckling of cold-formed sections." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0003/MQ39469.pdf.
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Chen, Yi 1975. "Local buckling behaviour of pultruded FRP composite sheet piles subjected to uniform pressure." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=98950.
Full textAbstract:
The buckling behaviour of fibre reinforced polymer (FRP) sheet pile panels subjected to a uniform lateral pressure was investigated. Based on the previous full scale tests by Shanmugan in year 2003 (Shanmugan, 2004), the critical load at buckling initiation was first determined through experimental data analysis, and the theoretical modeling was then followed in an attempt to predict the buckling initiation and understanding the failure mechanism. The behavior of the panels loaded in upright position and inverted position was studied.The local buckling of the compressive flanges was monitored by the strain measurements, which demonstrated that when tested in upright position, the panel failed immediately after local buckling of compressive flange, and when tested in inverted position, the panels could be able to carry the load into post buckling region. The stresses and corresponding axial forces at buckling were calculated by the classical beam flexure formula but taking into consideration the reduction of flexure rigidity and neutral axis shifting. The axial force calculated from the beam flexure formula was comparable with that from stain gauge measurements. The axial force was not uniformly distributed along the width of the compressive flange at upright position and was about zero at the free edge. When tested in inverted position, the neutral axis distance and the flexure rigidity kept almost as a constant. The sheet pile panels were with a uniform axial force along the width of the compressive flange.
An analytical modeling was performed to predict the buckling initiation. The buckling of the panel was simplified as the buckling of the compressive flange with various boundary conditions. The differential equation of the compressive flange was established based on the assumption that the flange was subjected to an in-plane axial force and an out-of-plane lateral pressure simultaneously. It was found that the lateral pressure did not have direct effect on the critical load. It was the compressive axial force that determined the local buckling of the flange. Kollar's explicit expressions were also applied but only valid for long plate loaded by uniform axial force.
The buckling load obtained by solving the differential equation for the inverted panel compared well with that from the experimental results. However, for the flange in a pile at an upright position, the theoretical prediction was far less than the experimental value which might be attributed to the non uniform axial force on the flange. Energy method was applied to estimate the range of the buckling load of a plate loaded by a linearly distributed axial force. The upper bound value was obtained from fixed boundary condition and the lower bound from simply supported assumption. The experimental result was found in between the two bounds and was in favour of the lower bound as a conservative estimation of critical load for upright panel.
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CINTRA, GISELE GOES. "LOCAL BUCKLING BEHAVIOR OF PULTRUDED GLASS-FIBER REINFORCED POLYMER (PGFRP) I-SECTION COLUMNS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36745@1.
Full textAbstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Este trabalho tem como objetivo investigar o desempenho de colunas com seção I em polímeros reforçados com fibra de vidro (pGFRP) submetidas a cargas de compressão concêntricas de curta duração. Uma revisão bibliográfica acerca das teorias existentes é apresentada, incluindo os conceitos básicos de instabilidade, teoria de flambagem global e local, modos de falha de colunas perfeitas, bem como o comportamento de colunas reais. Um programa experimental foi conduzido, incluindo a caracterização dos materiais. Vinte e nova colunas – com três diferentes seções I e diferentes tipos de resina, propriedades mecânicas, bem como comprimentos – foram testadas. Do ponto de vista global, as colunas foram biengastadas. As placas constituintes, por sua vez, foram testadas com três diferentes condições de contorno: biengastadas (CC), biapoiadas (SS) e simplesmente em contato com as chapas de base da máquina de compressão (CB). Foi observado que a condição de contorno CB – a mais adotada em estudos anteriores -, se aproxima mais de um engaste do que de uma condição simplesmente apoiada. A distribuição não linear de deformações elásticas ao longo da seção também foi investigada. Finalmente, recomendações para um ensaio de flambagem local apropriado foram propostas.
This work aims to investigate the performance of pultruded glass fiber reinforced polymer (pGFRP) I-section columns subject to short term concentric compression. A review of existing theories is presented, including the instability concepts, global and local buckling theories, perfect columns failure modes and the behavior of real columns. An experimental program including material characterization was conducted. Twenty-nine stubs – with three different I-sections geometries, having distinct flange width-to-section depth ratios (bf/d = 0.5; 0.75 and 1.0), mechanical properties, overall lengths and matrices – were tested. In a global point of view, the columns were fixed at both ends. The constituent plates, on the other hand, were tested with different end-conditions: clamped (CC), simply supported (SS) and simply in contact with base plates of the universal machine (CB). The third analyzed boundary condition, which is the most adopted in previous studies, was concluded to be closer to a clamped end-condition. The non-linear elastic strains distribution throughout the cross-section was also investigated. Finally, guideline recommendations for successful local buckling tests were proposed.
32
Ovesy, H. R. "The development and application of a semi-energy post-local buckling finite strip." Thesis, Cranfield University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.742420.
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Yap, Derrick. "Interaction of local and distortional buckling of high strength cold-formed steel columns." Thesis, The University of Sydney, 2008. https://hdl.handle.net/2123/28965.
Full textAbstract:
Thin—walled high strength cold—formed steel sections, when subjected to axial
compression, generally fail in a local, distortional and/or flexural—torsional buckling
mode. The sections can have a complex shape and can be fabricated from high strength
cold-formed steel with thickness as low as 0.42 mm. Such complex section designs
may lead to the interaction of local and distortional buckling modes when subjected to
axial compression.
The objective of the thesis is to investigate both theoretically and experimentally the
interaction of the local and distortional buckling modes of cold—formed steel channel
section columns in the post-distortional buckling range.
A theoretical study was carried out using the Finite Element Method (FEM) by
analysing the stress distributions in a simple-lipped channel section under compression.
A range of section thicknesses was analysed to observe sections failing in purely
distortional buckling modes and with interaction of local and distortional buckling
modes. Stress redistribution around the section in the postbuckling range was
observed in a method similar to von Karman’s approach. From the stress distributions
of the different sections, it was observed that when local and distortional buckling
interacts in the postbuckling range, the effect of the post—distortional buckling on the
post-local buckling stress is to push the stress higher at the flange-web junctions. This
observation explains the mechanics of a section subjected to interaction of local and
distortional buckling modes and why it may fail prematurely.
The thesis describes two series of tests performed on Stiffened-Web Channel (SWC)
section columns and Stiffened Cross-shaped (SCR) channel section columns fabricated
from high strength cold-formed steel sheets with thicknesses of 1 mm and 0.42 mm
respectively and a nominal yield stress of 550 MPa.
For the SWC section, a total of 14 fixed—ended columns were tested in compression to
study the local buckling failure of the short columns and the effect of the interaction of
local and distortional buckling on the intermediate and long columns. For the SCR
section, a total of 14 fixed-ended columns were tested to study the effect of the
interaction of local and multiple distortional buckling modes on the failure loads. The
effect of the inward and outward deflections in the distortional mode on failure was also
observed.
The test results are compared with structural design codes of the Australian Standard
AS/NZS 4600:2005 and the North American Specification (NAS) for cold—formed steel
structures. Both the Effective Width Method (EWM) and the Direct Strength Method
(DSM) were found to predict unconservatively for sections failing in the local buckling
mode. Further, the DSM predicts very unconservatively for sections failing in the
distortional mode when the interaction of local and distortional buckling modes occur.
Four new design methods are proposed to improve the local/overall and distortional
DSM strength curves. Conclusions on the most appropriate of the four methods and the
range of applicability are given.
34
Schillo, Nicole [Verfasser]. "Local and global buckling of box columns made of high strength steel / Nicole Schillo." Aachen : Shaker, 2017. http://d-nb.info/1138177393/34.
Full text
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Pokharel, Narayan. "Behaviour and design of sandwich panels subject to local buckling and flexural wrinkling effects." Thesis, Queensland University of Technology, 2003. https://eprints.qut.edu.au/15890/1/Narayan_Pokharel_Thesis.pdf.
Full textAbstract:
Sandwich panels comprise a thick, light-weight plastic foam such as polyurethane, polystyrene or mineral wool sandwiched between two relatively thin steel faces. One or both steel faces may be flat, lightly profiled or fully profiled. Until recently sandwich panel construction in Australia has been limited to cold-storage buildings due to the lack of design methods and data. However, in recent times, its use has increased significantly due to their widespread structural applications in building systems. Structural sandwich panels generally used in Australia comprise of polystyrene foam core and thinner (0.42 mm) and high strength (minimum yield stress of 550 MPa and reduced ductility) steel faces bonded together using separate adhesives. Sandwich panels exhibit various types of buckling behaviour depending on the types of faces used. Three types of buckling modes can be observed which are local buckling of plate elements of fully profiled faces, flexural wrinkling of flat and lightly profiled faces and mixed mode buckling of lightly profiled faces due to the interaction of local buckling and flexural wrinkling. To study the structural performance and develop appropriate design rules for sandwich panels, all these buckling failure modes have to be investigated thoroughly. A well established analytical solution exists for the design of flat faced sandwich panels, however, the design solutions for local buckling of fully profiled sandwich panels and mixed mode buckling of lightly profiled sandwich panels are not adequate. Therefore an extensive research program was undertaken to investigate the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. The first phase of this research was based on a series of laboratory experiments and numerical analyses of 50 foam-supported steel plate elements to study the local buckling behaviour of fully profiled sandwich panels made of thin steel faces and polystyrene foam core covering a wide range of b/t ratios. The current European design standard recommends the use of a modified effective width approach to include the local buckling effects in design. However, the experimental and numerical results revealed that this design method can predict reasonable strength for sandwich panels with low b/t ratios (< 100), but it predicts unconservative strengths for panels with slender plates (high b/t ratios). The use of sandwich panels with high b/t ratios is very common in practical design due to the increasing use of thinner and high strength steel plates. Therefore an improved design rule was developed based on the numerical results that can be used for fully profiled sandwich panels with any practical b/t ratio up to 600. The new improved design rule was validated using six full-scale experiments of profiled sandwich panels and hence can be used to develop safe and economical design solutions. The second phase of this research was based on a series of laboratory experiments and numerical analyses on lightly profiled sandwich panels to study the mixed mode buckling behaviour due to the interaction of local buckling and flexural wrinkling. The current wrinkling formula, which is a simple modification of the methods utilized for flat panels, does not consider the possible interaction between these two buckling modes. As the rib depth and width of flat plates between the ribs increase, flat plate buckling can occur leading to the failure of the entire panel due to the interaction between local buckling and wrinkling modes. Experimental and numerical results from this research confirmed that the current wrinkling formula for lightly profiled sandwich panels based on the elastic half-space method is inadequate in its present form. Hence an improved equation was developed based on validated finite element analysis results to take into account the interaction of the two buckling modes. This new interactive buckling formula can be used to determine the true value of interactive buckling stress for safe and economical design of lightly profiled sandwich panels. This thesis presents the details of experimental investigations and finite element analyses conducted to study the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. It includes development and validation of suitable numerical and experimental models, and the results. Current design rules are reviewed and new improved design rules are developed based on the results from this research.
36
Pokharel, Narayan. "Behaviour and Design of Sandwich Panels Subject to Local Buckling and Flexural Wrinkling Effects." Queensland University of Technology, 2003. http://eprints.qut.edu.au/15890/.
Full textAbstract:
Sandwich panels comprise a thick, light-weight plastic foam such as polyurethane, polystyrene or mineral wool sandwiched between two relatively thin steel faces. One or both steel faces may be flat, lightly profiled or fully profiled. Until recently sandwich panel construction in Australia has been limited to cold-storage buildings due to the lack of design methods and data. However, in recent times, its use has increased significantly due to their widespread structural applications in building systems. Structural sandwich panels generally used in Australia comprise of polystyrene foam core and thinner (0.42 mm) and high strength (minimum yield stress of 550 MPa and reduced ductility) steel faces bonded together using separate adhesives. Sandwich panels exhibit various types of buckling behaviour depending on the types of faces used. Three types of buckling modes can be observed which are local buckling of plate elements of fully profiled faces, flexural wrinkling of flat and lightly profiled faces and mixed mode buckling of lightly profiled faces due to the interaction of local buckling and flexural wrinkling. To study the structural performance and develop appropriate design rules for sandwich panels, all these buckling failure modes have to be investigated thoroughly. A well established analytical solution exists for the design of flat faced sandwich panels, however, the design solutions for local buckling of fully profiled sandwich panels and mixed mode buckling of lightly profiled sandwich panels are not adequate. Therefore an extensive research program was undertaken to investigate the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. The first phase of this research was based on a series of laboratory experiments and numerical analyses of 50 foam-supported steel plate elements to study the local buckling behaviour of fully profiled sandwich panels made of thin steel faces and polystyrene foam core covering a wide range of b/t ratios. The current European design standard recommends the use of a modified effective width approach to include the local buckling effects in design. However, the experimental and numerical results revealed that this design method can predict reasonable strength for sandwich panels with low b/t ratios (< 100), but it predicts unconservative strengths for panels with slender plates (high b/t ratios). The use of sandwich panels with high b/t ratios is very common in practical design due to the increasing use of thinner and high strength steel plates. Therefore an improved design rule was developed based on the numerical results that can be used for fully profiled sandwich panels with any practical b/t ratio up to 600. The new improved design rule was validated using six full-scale experiments of profiled sandwich panels and hence can be used to develop safe and economical design solutions. The second phase of this research was based on a series of laboratory experiments and numerical analyses on lightly profiled sandwich panels to study the mixed mode buckling behaviour due to the interaction of local buckling and flexural wrinkling. The current wrinkling formula, which is a simple modification of the methods utilized for flat panels, does not consider the possible interaction between these two buckling modes. As the rib depth and width of flat plates between the ribs increase, flat plate buckling can occur leading to the failure of the entire panel due to the interaction between local buckling and wrinkling modes. Experimental and numerical results from this research confirmed that the current wrinkling formula for lightly profiled sandwich panels based on the elastic half-space method is inadequate in its present form. Hence an improved equation was developed based on validated finite element analysis results to take into account the interaction of the two buckling modes. This new interactive buckling formula can be used to determine the true value of interactive buckling stress for safe and economical design of lightly profiled sandwich panels. This thesis presents the details of experimental investigations and finite element analyses conducted to study the local buckling behaviour of fully profiled sandwich panels and the mixed mode buckling behaviour of lightly profiled sandwich panels. It includes development and validation of suitable numerical and experimental models, and the results. Current design rules are reviewed and new improved design rules are developed based on the results from this research.
37
Lee, Jung Hoon. "Local buckling behaviour and design of cold-formed steel compression members at elevated temperatures." Thesis, Queensland University of Technology, 2004. https://eprints.qut.edu.au/15972/1/Jung_Hoon_Lee_Thesis.pdf.
Full textAbstract:
The importance of fire safety design has been realised due to the ever increasing loss of properties and lives caused by structural failures during fires. In recognition of the importance of fire safety design, extensive research has been undertaken in the field of fire safety of buildings and structures especially over the last couple of decades. In the same period, the development of fire safety engineering principles has brought significant reduction to the cost of fire protection. However the past fire research on steel structures has been limited to heavier, hot-rolled structural steel members and thus the structural behaviour of light gauge cold-formed steel members under fire conditions is not well understood. Since cold-formed steel structures have been commonly used for numerous applications and their use has increased rapidly in the last decade, the fire safety of cold-formed steel structural members has become an important issue. The current design standards for steel structures have simply included a list of reduction factors for the yield strength and elasticity modulus of hot-rolled steels without any detailed design procedures. It is not known whether these reduction factors are applicable to the commonly used thin, high strength steels in Australia. Further, the local buckling effects dominate the structural behaviour of light gauge cold-formed steel members. Therefore an extensive research program was undertaken at the Queensland University of Technology to investigate the local buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions.
The first phase of this research program included 189 tensile coupon tests including three steel grades and six thicknesses to obtain the accurate yield strength and elasticity modulus values at elevated temperatures because the deterioration of the mechanical properties is the major parameter in the structural design under fire conditions. The results obtained from the tensile tests were used to predict the ultimate strength of cold-formed steel members. An appropriate stress-strain model was also developed by considering the inelastic mechanical characteristics.
The second phase of this research was based on a series of more than 120 laboratory experiments and corresponding numerical analyses on cold-formed steel compression members to investigate the local bucking behaviour of the unstiffened flange elements, stiffened web elements and stiffened web and flange elements at elevated temperatures up to 800°C. The conventional effective design rules were first simply modified considering the reduced mechanical properties obtained from the tensile coupon tests and their adequacy was studied using the experimental and numerical results. It was found that the simply modified effective width design rules were adequate for low strength steel members and yet was not adequate for high strength cold-formed steel members due to the severe reduction of the ultimate strength in the post buckling strength range and the severe reduction ratio of the elasticity modulus to the yield strength at elevated temperatures. Due to the inadequacy of the current design rules, the theoretical, semi-empirical and empirical effective width design rules were developed to accurately predict the ultimate strength of cold-formed steel compression members subject to local buckling effects at elevated temperatures. The accuracy of these new design methods was verified by comparing their predictions with a variety of experimental and numerical results.
This thesis presents the details of extensive experimental and numerical studies undertaken in this research program and the results including comparison with simply modified effective width design rules. It also describes the advanced finite element models of cold-formed steel compression members developed in this research including the appropriate mechanical properties, initial imperfections, residual stresses and other significant factors. Finally, it presents the details of the new design methods proposed for the cold-formed steel compression members subject to local buckling effects at elevated temperatures.
38
Lee, Jung Hoon. "Local buckling behaviour and design of cold-formed steel compression members at elevated temperatures." Queensland University of Technology, 2004. http://eprints.qut.edu.au/15972/.
Full textAbstract:
The importance of fire safety design has been realised due to the ever increasing loss of properties and lives caused by structural failures during fires. In recognition of the importance of fire safety design, extensive research has been undertaken in the field of fire safety of buildings and structures especially over the last couple of decades. In the same period, the development of fire safety engineering principles has brought significant reduction to the cost of fire protection. However the past fire research on steel structures has been limited to heavier, hot-rolled structural steel members and thus the structural behaviour of light gauge cold-formed steel members under fire conditions is not well understood. Since cold-formed steel structures have been commonly used for numerous applications and their use has increased rapidly in the last decade, the fire safety of cold-formed steel structural members has become an important issue. The current design standards for steel structures have simply included a list of reduction factors for the yield strength and elasticity modulus of hot-rolled steels without any detailed design procedures. It is not known whether these reduction factors are applicable to the commonly used thin, high strength steels in Australia. Further, the local buckling effects dominate the structural behaviour of light gauge cold-formed steel members. Therefore an extensive research program was undertaken at the Queensland University of Technology to investigate the local buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. The first phase of this research program included 189 tensile coupon tests including three steel grades and six thicknesses to obtain the accurate yield strength and elasticity modulus values at elevated temperatures because the deterioration of the mechanical properties is the major parameter in the structural design under fire conditions. The results obtained from the tensile tests were used to predict the ultimate strength of cold-formed steel members. An appropriate stress-strain model was also developed by considering the inelastic mechanical characteristics. The second phase of this research was based on a series of more than 120 laboratory experiments and corresponding numerical analyses on cold-formed steel compression members to investigate the local bucking behaviour of the unstiffened flange elements, stiffened web elements and stiffened web and flange elements at elevated temperatures up to 800°C. The conventional effective design rules were first simply modified considering the reduced mechanical properties obtained from the tensile coupon tests and their adequacy was studied using the experimental and numerical results. It was found that the simply modified effective width design rules were adequate for low strength steel members and yet was not adequate for high strength cold-formed steel members due to the severe reduction of the ultimate strength in the post buckling strength range and the severe reduction ratio of the elasticity modulus to the yield strength at elevated temperatures. Due to the inadequacy of the current design rules, the theoretical, semi-empirical and empirical effective width design rules were developed to accurately predict the ultimate strength of cold-formed steel compression members subject to local buckling effects at elevated temperatures. The accuracy of these new design methods was verified by comparing their predictions with a variety of experimental and numerical results. This thesis presents the details of extensive experimental and numerical studies undertaken in this research program and the results including comparison with simply modified effective width design rules. It also describes the advanced finite element models of cold-formed steel compression members developed in this research including the appropriate mechanical properties, initial imperfections, residual stresses and other significant factors. Finally, it presents the details of the new design methods proposed for the cold-formed steel compression members subject to local buckling effects at elevated temperatures.
39
Fagerberg, Linus. "Wrinkling of sandwich panels for marine applications." Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3587.
Full textAbstract:
The recent development in the marine industry with largerships built in sandwich construction and also the use of moreadvanced materials has enforced improvements of design criteriaregarding wrinkling. The commonly used Hoffs formula isnot suited for the highly anisotropic fibre reinforced sandwichface sheets of today.
The work presented herein investigates the wrinklingphenomenon. A solution to wrinkling of anisotropic sandwichplates subjected to multi-axial loading is presented. Thesolution includes the possibility of skew wrinkling where thewrinkling waves are not perpendicular to the principal loaddirection. The wrinkling angle is obtained from the solutiontogether with the maximum wrinkling load. This method has beensupported with tests of anisotropic plates subjected touni-axial and bi-axial loading.
The effect of the face sheet local bending stiffness showsthe importance of including the face sheet stacking sequence inthe wrinkling analysis. The work points out the influence ofthe face sheet local bending stiffness on wrinkling. Threedifferent means of improving the wrinkling load except changingcore material is evaluated. The effect of the differentapproaches is evaluated theoretically and also throughcomparative testing. The transition between wrinkling and pureface sheet compression failure is investigated. Theoreticaldiscussions are compared with compressive test results of twodifferent face sheet types on seven different core densities.The failure modes are investigated using fractography. Theresults clearly show how the actual sandwich compressionfailure mode is influenced by the choice of core material,changing from wrinkling failure to face sheet micro bucklingfailure as the modulus density increases.
Finally, a new approach is presented where the wrinklingproblem is transferred from a pure stability problem to amaterial strength criterion. The developed theory providesmeans on how to decide which sandwich constituent will failfirst and at which load it will fail. The method give insightto and develop the overall understanding of the wrinklingphenomenon. A very good correlation is found when the developedtheory is compared with both finite element calculations and toexperimental tests.
Keywords:wrinkling, local buckling, imperfection,stability, anisotropy, sandwich
40
Huynh, Le Anh Thi. "Strength and Behaviour of Cold-rolled Aluminium Sections." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21549.
Full textAbstract:
This thesis presents a comprehensive study on the strength and the behaviour of cold-rolled aluminium sections in compression and bending. The first step of the research project focused on the investigation of mechanical properties and residual stresses in cold-rolled aluminium channel sections. Subsequently, both experimental and numerical investigations were performed to investigate the behaviour and sectional capacities. Finally, design rules based on the Direct Strength Method for cold-rolled aluminium columns and beams were proposed in this thesis. The experimental study encompassed three test series including mechanical property, column and beam experiments. All specimens chosen for the experimental program were roll-formed and supplied by BlueScope Permalite, Australia using aluminium alloy 5052-H36 coils. Thorough investigations of the distributions of mechanical properties and residual stresses in the cross-sections were carried out from three different cold-rolled aluminium C-sections. A total number of 227 coupon tests including 198 flat tension coupon tests, 20 corner tension coupon tests and 9 flat compression coupon tests were conducted. The residual stresses were measured from a total number of 9 cold-rolled aluminium channel sections of three different cross-sections. For section capacity experiments, the test series for columns was conducted on 21 column specimens, which consisted of 12 stub columns subjected to local buckling and 9 intermediate-length columns subjected to distortional buckling of three different cross-sections. The test series for beams comprised 18 bending tests undergoing local buckling and 18 bending tests undergoing distortional buckling of four different cross-section types including channel, down-lip channel, zed and down-lip zed section. Three different channel cross-sections, which were selected in column tests, also were used in beam test to further understand the behaviour of this aluminium members. The local and overall geometric imperfections for all specimens were measured prior to test. For numerical non-linear simulation, the finite element program ABAQUS was used to simulate the behaviour of cold-rolled aluminium sections in both compression and bending. Detailed finite element (FE) models were developed including non-linear material behaviour, actual initial geometric imperfections and forming-induced residual stresses. The simulation results were compared and validated against the four experimental series. The FE models were subsequently used for a parametric study to extend the database of cross-section geometries of columns and beams undergoing local and distortional buckling. In design section, the experiment and FE results were compared with the current design codes from American, Australian/New Zealand and European Standards/ Specifications for aluminium structures. Additionally, the Direct Strength Method (DSM), which has been developed for cold-formed steel structures and stainless steel, was used in this study for predicting cold-rolled aluminium alloy section capacities of columns and beams. Finally, the revised format Direct Strength Method formulae were derived and proposed to better fit the data and give more accurate predictions. The proposed formulae offered simple design solutions, which fit within the current Load and Resistance Factor Design (LRFD) framework. The reliability of the current and proposed design rules was evaluated using reliability analysis.
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Mysore, Paramesh Pragati. "Feasibility Study on Highly Slender Circular Concrete Filled Tubes Under Axial Compression." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/75045.
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Circular Concrete Filled Tubes are gaining importance in the construction industry due to their advantages insofar as economy and structural efficiency. Due to the recent developments in concrete and steel technology, the usage of high strength materials in these concrete filled tubes is increasing. The governing American specification (AISC 360-16) classifies these composite members as compact, non-compact and slender sections. The allowed section slenderness (ratio of diameter to thickness ratio) in each classification is related to the material properties (ratio of Young's modulus to yield strength ratio). AISC 360-16 is applicable for steels up to 75 ksi and concretes up to 10 ksi. These limits are lower than current available materials and restricts the usage of highly slender sections. As the strength of these tubes is dependent on local buckling, tests on many combinations of high strength steel and concrete are needed to extend these material limits.
This preliminary research work focuses on understanding the local buckling behavior of highly slender sections and the effect of concrete infill and its confinement. The research began by compiling a database that highlighted a gap on tests with highly slender sections and high strength materials. To address this issue, a pilot set of experimental tests were conducted on short circular concrete filled members. An analytical evaluation of these experimental results are performed using 3D finite element analysis models. The critical buckling load is determined using J2 deformation theory, which proves to give a good estimate when compared with the experimental results. The main objective of the work is to determine if a simplified test like the one used in this work could be used for the large experimental study that will be necessary to expend the material limits in AISC 360-16. The limited data developed in this study indicates that the test can provide satisfactory results with a few improvements and refinements.Master of Science
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Mahenthirarasa, Rokilan. "Cold-formed steel compression members exposed to extreme temperature environments." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/226125/1/Rokilan_Mahenthirarasa_Thesis.pdf.
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This thesis investigated the behaviour of cold-formed steel compression members under extreme temperature environments using experimental and numerical studies. It proposed both new and improved design models for (1) the elevated and sub-zero temperature mechanical properties of cold-formed steels and (2) the compression capacities of cold-formed steel members exposed to uniform and non-uniform elevated temperatures and uniform sub-zero temperatures. The proposed design models are likely to be adopted by the Australian and American cold-formed steel structures standards, while the new knowledge will enable increased applications of cold-formed steel members in the building industry.
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Schillo, Nicole Verfasser], Markus [Akademischer Betreuer] [Feldmann, and Andreas [Akademischer Betreuer] Taras. "Local and global buckling of box columns made of high strength steel / Nicole Schillo ; Markus Feldmann, Andreas Taras." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162499257/34.
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Schillo, Nicole [Verfasser], Markus [Akademischer Betreuer] Feldmann, and Andreas [Akademischer Betreuer] Taras. "Local and global buckling of box columns made of high strength steel / Nicole Schillo ; Markus Feldmann, Andreas Taras." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://nbn-resolving.de/urn:nbn:de:101:1-2018071007084306056654.
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Nuttayasakul, Nuthaporn. "Experimental and Analytical Studies of the Behavior of Cold-Formed Steel Roof Truss Elements." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29765.
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Cold-formed steel roof truss systems that use complex stiffener patterns in existing hat shape members for both top and bottom chord elements are a growing trend in the North American steel framing industry. When designing cold-formed steel sections, a structural engineer typically tries to improve the local buckling behavior of the cold-formed steel elements. The complex hat shape has proved to limit the negative influence of local buckling, however, distortional buckling can be the controlling mode of failure in the design of chord members with intermediate unbraced lengths. The chord member may be subjected to both bending and compression because of the continuity of the top and bottom chords. These members are not typically braced between panel points in a truss.
Current 2001 North American Specifications (NAS 2001) do not provide an explicit check for distortional buckling. This dissertation focuses on the behavior of complex hat shape members commonly used for both the top and bottom chord elements of a cold-formed steel truss. The results of flexural tests of complex hat shape members are described. In addition, stub column tests of nested C-sections used as web members and full scale cold-formed steel roof truss tests are reported.
Numerical analyses using finite strip and finite element procedures were developed for the complex hat shape chord member in bending to compare with experimental results. Both elastic buckling and inelastic postbuckling finite element analyses were performed. A parametric study was also conducted to investigate the factors that affect the ultimate strength behavior of a particular complex hat shape.
The experimental results and numerical analyses confirmed that modifications to the 2001 North American Specification are necessary to better predict the flexural strength of complex hat shape members, especially those members subjected to distortional buckling. Either finite strip or finite element analysis can be used to better predict the flexural strength of complex hat shape members. Better understanding of the flexural behavior of these complex hat shapes is necessary to obtain efficient, safe design of a truss system. The results of these analyses will be presented in the dissertation.Ph. D.
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YANG, Demao. "Compression Stability of High Strength Steel Sections with Low Strain-Hardening." University of Sydney. School of Civil Engineering, 2003. http://hdl.handle.net/2123/561.
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Thin-walled steel sections made from high strength thin cold-reduced G550 steel to Australian Standard AS 1397-1993 under compression are investigated experimentally and theoretically in this thesis. This thesis describes three series of compression tests performed on box-section stub columns, box-section long columns and lipped channel section columns cold-formed from high strength steel plates in 0.42 mm or 0.60 mm thickness with nominal yield stress of 550 MPa. The tests presented in this thesis formed part of an Australian Research Council research project entitled: Compression Stability of High Strength Steel Sections with Low Strain-Hardening. For the fix-ended stub column tests, a total of 94 lipped-square and hexagonal section stub columns were tested to study the influence of low strain hardening of G550 steel on the compressive section capacities of the column members. For the pin-ended long column tests, a total of 28 box-section columns were tested to study the stability of members with sections which undergo local instability at loads significantly less than the ultimate loads. For the fix-ended lipped channel section columns, a total of 21 stub and long columns were tested to study the failure resulting from local and distortional buckling with interaction between the modes. A numerical simulation on the three series of tests using the commercial finite element computer program ABAQUS is also presented as part of this thesis. The post-buckling behaviour of thin-walled compression members is investigated. The effect of changing variables, such as geometric imperfections and end boundary conditions is also investigated. The ABAQUS analysis gives accurate simulations of the tests and is in good agreement to the experimental results. Theoretical studies using finite strip methods are presented in this thesis to investigate the buckling behaviour of cold-formed members in compression. The theoretical studies provide valuable information on the local and distortional buckling stresses for use in the interaction buckling studies. The finite strip models used are the semi-analytical and spline models. As expected for the stub columns tests, the greatest effect of low strain hardening was for the stockier sections where material properties play an important role. For the more slender sections where elastic local buckling and post-local buckling are more important, the effect of low strain hardening does not appear to be as significant. The pin-ended and fix-ended long column tests show that interaction, which is between local and overall buckling in the box sections, and between local and distortional buckling in the open channel sections, has a significant effect on their member capacities. The results of the successful column tests and ABAQUS simulation have been compared with the design procedures in the Australian & New Zealand Standard for Cold-Formed Steel Structures AS&NZS 4600 and the North American Specification for Cold-Formed Steel Structural Members prepared by the American Iron and Steel Institute. The stub column tests show that the current design rules give too conservative predictions on the compressive section capacities of the column members; whereas the long column tests show that the current column design rules are unconservative if used in their current form for G550 steel. Three design proposals are presented in this thesis to account for the effects of high strength thin steels on the section and member capacities.
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Amarante, Rodrigo de Almeida. "Compressão dinâmica em risers." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3135/tde-11082015-154505/.
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O presente trabalho foi realizado por meio de uma abordagem tríplice do problema de compressão dinâmica em risers, fundamentado em ensaios em um Calibrador Hidrodinâmico, com posterior confrontação dos resultados com formulações analíticas e o uso de programas comerciais dedicados ao estudo da estática e dinâmica de linhas flexíveis. O principal objetivo foi a determinação acurada, a partir de uma instrumentação pouco invasiva, dos comprimentos das ondas de flexão geradas no TDP, durante a compressão dinâmica. Esse objetivo, de per si, encerra o caráter de ineditismo da presente tese. Os ensaios consistiram na realização de movimentos circulares no topo de um modelo flexível lançado em catenária, sob diversas configurações, totalizando um total de 72 experimentos: foram utilizados três frequências de movimento, três amplitudes, quatro ângulos de topo e dois sentidos de rotação. Um sistema de monitoramento óptico foi utilizado como principal instrumentação. Além desse equipamento, foi utilizada uma célula de carga, posicionada entre o equipamento que prescrevia os movimentos ao modelo flexível e uma rótula, que permitia que a célula de cargas e movimentasse solidariamente ao sistema. Rotinas numérica próprias foram utilizadas para o pós-processamento dos dados obtidos. Os resultados foram, então, comparados com formulações analíticas constantes da literatura, bem como a adaptação da equação para a carga crítica de flambagem de vigas curvas, para as condições de contorno dos ensaios realizados. Como resultado principal, é possível citar a confirmação experimental da suposição corrente com relação ao número de onda associado às ondas de flexão geradas na compressão dinâmica, até então assumida como uma hipótese ad hoc. Além disso, o procedimento adotado, embasado teoricamente, foi utilizado desde o estabelecimento do material com que o modelo foi construído, passando pela elaboração racional da matriz de ensaios e finalizando com as análises realizadas, quando os resultados experimentais foram confrontados com as previsões analíticas.This work was carried out through a threefold approach to dynamic compression in risers, based on tests in a Hydrodynamic Calibrator, with subsequent comparison of results with analytical formulations and the use of commercial softwares dedicated to the study of static and dynamic flexible lines. The main aim was an accurate determination, from a minimally invasive instrumentation, the lengths of flexural waves generated in the TDP, during dynamic compression. This goal, in itself, is the novelty of this thesis. The tests consisted in performing circular motion on top of a flexible catenary model launched under several conditions, amounting to a total of 72 experiments: three motion frequencies, three imposed amplitudes , four top angles and clockwise and counter-clockwise rotation. A tracking monitoring system was used as main instrumentation. In such equipment, a load cell was used, positioned between rotor used to prescribe top movements at the top of a flexible model, allowing the load cell jointly move around a bar conected to the shaft motor. Numerical routines, made by author, were used for data post-processing. The results were then confronted with analytical formulations from specialized literature, as well as the adaptation of the equation for the buckling critical load for curved beams under the boundary conditions of the tests. As a main result, it is possible to mention the experimental confirmation of the current assumption with respect to the wave number associated with bending waves generated during the dynamic compression, hitherto assumed as an ad hoc hypothesis. In addition, the procedure adopted, based in analytical theories, was used since the establishment of the material with which the model is built, through the rational development of the test matrix and ending with the analyzes carried out when the experimental results were compared with analytical predictions.
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Cheng, Shanshan. "Fire performance of cold-formed steel sections." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3316.
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Thin-walled cold-formed steel (CFS) has exhibited inherent structural and architectural advantages over other constructional materials, for example, high strength-to-weight ratio, ease of fabrication, economy in transportation and the flexibility of sectional profiles, which make CFS ideal for modern residential and industrial buildings. They have been increasingly used as purlins as the intermediate members in a roof system, or load-bearing components in low- and mid-rise buildings. However, using CFS members in building structures has been facing challenges due to the lack of knowledge to the fire performance of CFS at elevated temperatures and the lack of fire design guidelines. Among all available design specifications of CFS, EN1993-1-2 is the only one which provided design guidelines for CFS at elevated temperatures, which, however, is based on the same theory and material properties of hot-rolled steel. Since the material properties of CFS are found to be considerably different from those of hot-rolled steel, the applicability of hot-rolled steel design guidelines into CFS needs to be verified. Besides, the effect of non-uniform temperature distribution on the failure of CFS members is not properly addressed in literature and has not been specified in the existing design guidelines. Therefore, a better understanding of fire performance of CFS members is of great significance to further explore the potential application of CFS. Since CFS members are always with thin thickness (normally from 0.9 to 8 mm), open cross-section, and great flexural rigidity about one axis at the expense of low flexural rigidity about a perpendicular axis, the members are usually susceptible to various buckling modes which often govern the ultimate failure of CFS members. When CFS members are exposed to a fire, not only the reduced mechanical properties will influence the buckling capacity of CFS members, but also the thermal strains which can lead additional stresses in loaded members. The buckling behaviour of the member can be analysed based on uniformly reduced material properties when the member is unprotected or uniformly protected surrounded by a fire that the temperature distribution within the member is uniform. However if the temperature distribution in a member is not uniform, which usually happens in walls and/or roof panels when CFS members are protected by plaster boards and exposed to fire on one side, the analysis of the member becomes very complicated since the mechanical properties such as Young’s modulus and yield strength and thermal strains vary within the member. This project has the aim of providing better understanding of the buckling performance of CFS channel members under non-uniform temperatures. The primary objective is to investigate the fire performance of plasterboard protected CFS members exposed to fire on one side, in the aspects of pre-buckling stress distribution, elastic buckling behaviour and nonlinear failure models. Heat transfer analyses of one-side protected CFS members have been conducted firstly to investigate the temperature distributions within the cross-section, which have been applied to the analytical study for the prediction of flexural buckling loads of CFS columns at elevated temperatures. A simplified numerical method based on the second order elastic – plastic analysis has also been proposed for the calculation of the flexural buckling load of CFS columns under non-uniform temperature distributions. The effects of temperature distributions and stress-strain relationships on the flexure buckling of CFS columns are discussed. Afterwards a modified finite strip method combined with the classical Fourier series solutions have been presented to investigate the elastic buckling behaviour of CFS members at elevated temperatures, in which the effects of temperatures on both strain and mechanical properties have been considered. The variations of the elastic buckling loads/moments, buckling modes and slenderness of CFS columns/beams with increasing temperatures have been examined. The finite element method is also used to carry out the failure analysis of one-side protected beams at elevated temperatures. The effects of geometric imperfection, stress-strain relationships and temperature distributions on the ultimate moment capacities of CFS beams under uniform and non-uniform temperature distributions are examined. At the end the direct strength method based design methods have been discussed and corresponding recommendations for the designing of CFS beams at elevated temperatures are presented. This thesis has contributed to improve the knowledge of the buckling and failure behaviour of CFS members at elevated temperatures, and the essential data provided in the numerical studies has laid the foundation for further design-oriented studies.
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Perera, Nilakshi. "Structural behaviour and design of innovative hollow flange steel plate grinders." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/123310/1/Liyanage%20Nilakshi%20Piyahasi_Perera_Thesis.pdf.
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This thesis proposes a new Hollow Flange Steel Plate Girder (HFSPG) by welding industrially available cold-formed Rectangular Hollow Sections (RHS) to a web plate for use in long span construction. Design procedures presented in the national and international design guidelines were reviewed and suitable improvements were made to accurately predict the structural behaviour and capacities of HFSPGs by undertaking detailed experimental and numerical studies into their unique structural behaviour. Local buckling/yielding, global buckling and local-global interaction failures were all considered in this thesis.
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Nguyen, The Nguyen. "Flambage sous contact d’une coque cylindrique soumise à pression externe." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI070/document.
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Cette étude vise à analyser la coque qui est en contact avec un matériau qui la confine, et qu’elle subite une pression latérale externe. Les conditions de contact entre les deux corps, frottant ou pas, la rigidité du confinement ainsi que les conditions de chargement, la pression qui peut être directement appliquée à la coque comme elle peut être induite par le matériau de confinement qui par retrait ou retreint ou convergence radiale induit des contraintes, ceux sont là les paramètres qui nous paraissent essentiels à jauger pour la problématique du flambage avec contact d’une coque sous pression externe. Une campagne expérimentale où plusieurs configurations de confinement sont considérées. La nature du milieu extérieur associé au confinement et donc sa rigidité, le type de confinement, discret ou locale au bien total (surface entière de la coque), sont évalués. Une instrumentation adéquate, couplant des mesures ponctuelles et de champ nous a permis de correctement mettre en exergue la phénoménologie. Les simulations numériques par éléments finis à l’aide du code de calcul Abaqus/Standard 6.12-3 intègrent les différentes non linéarité mise en musique dans ce problème, les grands déplacements et rotations du fait du flambage, la non linéarité matériau. Ces travaux montrent que même pour un confinement externe avec une très faible rigidité de membrane, comme pour le sable ou le polystyrène expansé, un gain important de capacité portante est observé, le flambage est retardé. L’augmentation est substantielle dans le cas d’un confinement total, non négligeable et consistante dans le cas d’un confinement local. Nous avons aussi constaté que la charge de flambage et le mode associé dépendent de la configuration de contact, notamment de la rigidité à la flexion du confinementMotivated by practical engineering applications, thin-walled cylindrical shells are widely used as structural elements. Because of their low flexural strength, these structures are very sensitive to buckling when exposed to external pressur. Conventional stiffening which makes it possible to improve the bearing capacity is to add stiffening rings connected by axial stiffeners or axial stiffeners. In these configurations the stiffening elements are an integral part of the structure with a continuity of material. One can ask the question of the effect of contiguous but non-continuous adjacent external structures ensuring total or local surface external contact. These are real configurations, such as those of buried pipelines, pipelines, or the case of insulated structures. This study aims to analyze these cases where the shell is in contact with a material which confines it, and that it undergoes an external lateral pressure. The contact conditions between the two bodies, whether rubbing or not, the stiffness of the confinement as well as the loading conditions, the pressure which can be directly applied to the shell as it may be induced by the confinement material which by withdrawal or shrinkage or Radial convergence induces stresses, these are the parameters that we consider essential for gauging the problem of buckling with contact of an external pressure shell. To answer these questions, we conducted an experimental campaign where several configurations of confinement are considered. The nature of the external environment associated with the confinement and therefore its rigidity, the type of confinement, discrete local or the total property (entire surface of the shell), are evaluated. Appropriate instrumentation, coupling point and field measurements, has allowed us to correctly highlight the phenomenology. Numerical modeling is also carried out using finite element method by Abaqus/Standard 6.12-3 code. Numerical simulations integrate the different nonlinearities in this problem, large displacements and rotations due to buckling, nonlinearity material, in some cases the buckling is plastic, but also the nonlinearity induced by an evolutionary contact. The modeling is carried out in 2D and 3D mesh, and in the latter case either by means of shell elements or by massive elements, the first aim being to corroborate the experimental observations more or less precisely. This work shows that even for external confinement with very low membrane rigidity, as for sand or expanded polystyrene, a significant gain in bearing capacity is observed, the buckling is delayed. The increase is substantial in the case of a total confinement which is not negligible and consistent in the case of local confinement. We have also found that the buckling load and the associated mode depend on the contact configuration, in particular the flexural rigidity of the confinement